This invention generally relates to compressor control systems, and more particularly to a capacity control system for a rotary screw compressor.
The application of helical screw compressors for supplying compressed air to pneumatic construction equipment and to industrial plant compressed air networks usually requires that the compressor be equipped with some form of compressor throughput or capacity control. A turn valve or spiral valve is a well known device for efficiently controlling capacity in a rotary screw compressor. Heretofore, turn valves typically have been controlled by such systems as a rack and pinion system having a piston at each end of the rack. Typically, these pistons are enclosed in a cylinder, and are controlled by a suitable actuating fluid, such as air or a hydraulic fluid, for example. In such a capacity control system, a control valve directs fluid pressure to a piston on a predetermined side of the rack to open or close the turn valve. However, while such compressor capacity control systems may be useful in their purpose, they are replete with a multiplicity of deficiencies and shortcomings which have detracted from their usefulness.
Foremost among the deficiencies attributable to such compressor control systems is their apparent inability to reach a steady state condition. Such compressor control systems must always be either opening or closing the turn valve. Additionally, such controls are typically prone to leaks of actuating fluid. Further, these controls may require cumbersome and complex actuating fluid lines. Finally, such compressor control systems are costly, and require careful calibration to function for their intended purposes.
The foregoing illustrates limitations known to exist in present capacity control systems for rotary screw compressors. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.